Generally, a semiconductor device is formed by fabricating a silicon wafer, and respective chips are packaged with epoxy or the like so as to be used as electronic parts. In accordance with the trend of miniaturizing electronic apparatuses, attempts are being made to achieve high density semiconductor devices. Therefore, the package itself is being more and more miniaturized, and attempts are being made to pack one or more chips into one package.
The stack chip package (SCP) is one such conventional package. As illustrated in FIG. 1, such a package uses a mirror type semiconductor chip having a different: pad layout structure which is formed by taking into account the desired electrical connections. The package has upper chip 11 and lower chip 12 arranged up and down, inner leads 13 connected to pads of the semiconductor chips, respectively, outer leads 14 connected to the inner leads, respectively, by laser-welding, and a molding compound such as epoxy.
In order to manufacture the package of such a structure, the wafer for which the fabrication has been completed is subjected to a sawing, and solder bumps are attached on bonding pads. By utilizing the solder bumps, the inner leads are connected to the bonding pads, and two such chips are disposed symmetrically above and below. The inner leads and the outer leads are laser-welded together, a molding is carried out, and the outer leads are trimmed and formed, thereby completing the package.
In this package, however, in order to form an electrical connection between the inner leads of the upper and lower chips and the outer leads, the layout of the upper and lower bonding pads of the upper chip and lower chip should take a mirror form. Therefore, two mutually different chip layouts are required, and the inner leads and the outer leads are laser-welded by placing them face to face with each other for each pair. Therefore, a highly difficult technique is required, and thus the productivity becomes low, while new equipment also is required. Further, a first step of trimming and forming the inner leads is carried out, and a second step of trimming and forming the outer leads is carried out. Therefore, the process is complicated, and the yield is low, while automation becomes difficult in view of the nature of the technique.